<!DOCTYPE html>
<html lang="zh-hans">
<head>
  <meta charset="UTF-8">
  <title>红绿灯</title>
  <link rel="stylesheet" href="traffic-lights.css">
</head>
<body>
  <div class="traffic-lights">
    <div class="red-on">60</div>
    <div class="yellow-on">60</div>
    <div class="green-on">60</div>
  </div>
</body>
</html>